Sports Balls Research Articles

Football boundary-layer separation via dust experiments

A method of examining the separation of the boundary layer of air from a sports ball, specifically a football, is presented. Using a ball launcher, a non-spinning football is fired into a dust cloud. A high-speed camera records the ball passing through the dust cloud. Unlike wind-tunnel methods, the dust method described here allows for the examination of the boundary-layer separation without a ball-supporting arrangement. Boundary-layer separation for speeds surrounding the drag crisis is studied. Though the general trend is for the boundary layer to separate farther back on the ball as the ball’s centre-of-mass speed increases, anomalous behaviour is seen just past the drag crisis, namely a rise in the separation angle, followed by an expected decrease.

Effect of temperature on the dynamic properties of soccer balls

Soccer is played over a wide range of temperatures. Previous research has shown that the dynamic properties of sports balls, such as squash balls, tennis balls, and baseballs are dependent on temperature. The aim of this research was to determine whether the dynamic properties of soccer balls are temperature dependent. Quasi-static tensile testing was conducted on samples of soccer ball material, at nominal temperatures of 0, 20, and 40 °C. Normal impact testing at speeds up to 22 m/s was undertaken at nominal ball temperatures of 0, 20, and 40 °C. The stiffness of the material decreased as the temperature increased. The coefficient of restitution, contact time, and maximum deformation of the ball all increased with temperature. The mean coefficient of restitution was 0.82 ± 0.03 at 40 °C in comparison to 0.73 ± 0.02 at 0 °C. A foot-to-ball impact model combined with a trajectory model was used to simulate a penalty kick directed at the top corner of the goal. The results showed that the time available to the goalkeeper was 7 per cent shorter at 40 °C in comparison to that at 0 °C. Therefore, the time available for a goalkeeper to prevent a goal decreases as temperature increases.

Viscoelastic impact characterisation of solid sports balls used in the Irish sport of Hurling

In recent years, variability in behaviour of the sliotar, a small leather-bound ball used in the Irish sport of hurling, has become evident in championship matches. The inconsistency in performance was attributed to the range of constructions and material compositions of currently approved ball types. With a view to adopting a standard core, a new methodology has been commissioned to assess the dynamic impact behaviour of approved sliotar cores. In this paper, the relationship between the dynamic stiffness and the coefficient of restitution is presented with regard to material properties, ball construction and viscoelastic strain and strain-rate dependencies. The modern polymer ball types were shown to exhibit strain-rate sensitivity, while the performance of the traditional multi-compositional ball types exhibited lesser strain-rate dependence. The traditional balls types were shown to be up to 2.5 times stiffer than the modern ball types, with this finding having implications for ball energy dissipation.

The effect of temperature and humidity on the performance of baseballs and softballs

Sports balls such as softballs and baseballs are made from materials that are natural (cork, wool, leather) and synthetic (rubber, polyurethane) and are sensitive to moisture and temperature. It is common practice, for instance, for major league baseball parks in dry climates to condition their baseballs at 50% relative humidity. Baseball and softball are played at temperatures ranging from less than 4C (40 F) to more than 38C (100 F). Standardized ball tests require controlled temperature and humidity test environments. Little information is available, however, to quantity the effect of temperature and humidity on a ball's response. The following describes test procedures used to condition softballs and baseballs to controlled levels of humidity and temperature and their effect on the ball's stiffness and elasticity. While the construction of the baseballs and softballs are quite different, their elasticity and stiffness show a similar trend with temperature and humidity. Their combined effect was shown to lower bat performance as both temperature and humidity were increased.

In situ lift measurement of sports balls

Aerodynamic lift on sports balls is typically measured in wind tunnels. Wind tunnel measurements may have measurable differences with ball drag occurring in play. Measurements under game conditions have been attempted, but are difficult to interpret from the data scatter and are not controlled. The following considers lift measurements from a ball propelled through static air in a laboratory setting. High speed light gates were used to measure lift. Lift was observed to depend on the ball speed, roughness, stitch height, and orientation.

A novel sports ball aerodynamics analysis tool: soccer ball design

A novel soccer ball design tool involving the optimisation of the aerodynamics is developed in this paper. The design tool allows the flight of different balls with various input conditions to be compared and the behaviour of new ball designs to be assessed. The tool was developed by combining CFD results with information from wind tunnel tests, trajectory testing, and player testing. Subsequently, the results (force coefficient data) were entered into a trajectory simulation programme. Various soccer ball designs were assessed using the design tool, and several conclusions drawn regarding aerodynamic optimisation. Two kick types are studied in this paper: curling, high-spinning kicks that are typically used for free-kicks, corners and long passes, and erratic, high-velocity, low-spinning kicks that are typically used for free-kicks, and shots on goal. The key physical phenomena relevant to both kick types were identified, and related to real game situations. Curling kicks were found to experience more sw...

Laser tracking system for sports ball trajectory measurement

The sports ball market is a multi-million dollar industry; original equipment manufacturers are continually trying to develop sports balls and in order to achieve improvement in performance they often utilize launch and/or flight monitors to allow consistent measurement and benchmarking of their balls under test. This paper introduces a laser tracking system (LTS), which has been specifically designed for soccer ball tracking. This LTS combines two different concepts together in an innovative optical solution to allow the system to track an arbitrarily moving soccer ball in a completely non-contact and non-marking methodology, tracking a ball in real time up to approximately 10m/s. The system was programmed to act as a launch monitor capable of reporting the ball launch velocity and launch angle. In order to achieve the fully functional LTS, the hardware and software choices are clearly outlined, as well as describing the tracking methodology used to achieve the real-time tracking capability.

In situ drag measurements of sports balls

Aerodynamic drag on sports balls is typically measured in wind tunnels. There is a concern that fixtures needed to support the ball in a wind tunnel may influence its drag. Measurements under game conditions have been attempted, but are difficult to interpret from the data scatter and are not controlled. The following considers drag measurements from a ball propelled through static air in a laboratory setting. High speed light gates were used to measure drag, including the effects of ball rotation. Drag was observed to depend on the ball speed, rotation, roughness, and orientation. A so-called drag crisis was observed for a smooth sphere and was comparable to wind tunnel data. Rough sports balls, such as a baseball, showed evidence of a small drag crisis that was less apparent than the smooth sphere.

Finite element modelling of the quasi-static and dynamic behaviour of a solid sports ball based on component material properties

Finite element modelling (FEM) has been used to replicate the quasi-static and dynamic behaviour of a solid sports ball (of a single material, extracted from a commercial hockey ball), by using experimentally determined viscoelastic, hyperelastic and mechanical material properties and data obtained from the ball material. Material data were measured using cylinders extracted from the ball. Hyperelastic data were obtained in uniaxial quasi-static compression, performed at a strain rate of 2×10−5 s−1, with viscoelastic data obtained in uniaxial compressive stress relaxation testing (at a range of strains between 0.05–0.2, to assess linear/non-linear viscoelasticity). The model assumes that the material properties were isotropic and its behaviour could be accurately described by a hyperelastic strain energy function and a viscoelastic Prony series. The accuracy of experimental stress relaxation data is discussed, along with its suitability for obtaining viscoelastic properties for use in modelling the quasi-static and dynamic behaviour of solid sports balls.

Development and performance of a ball shooting machine

Wind tunnels are often used when investigating the aerodynamic characteristics of sports balls, and have proven to be effective experimental equipment. However, wind tunnel experiments are fundamentally targeted at testing fixed steady states, so in some cases ball ejection units capable of unsteady states are needed. This research undertook the design and development of an impact type ball ejection unit with stable initial parameters and striking characteristics that make variable-state testing of sports balls possible. The kick arm swings due to an actuator activated by air-pressure, impacting a fixed ball. The swing action itself has 1 degree of freedom; however, there are 3 degrees of freedom for the alignment of the striker. The soccer ball may achieve a maximum velocity of 131 km/h when ejected, allowing a shooting speed of 100 km/h when the unit is operating at 70% power. Further, it was found that there was a direct correlation between impact velocity and the initial velocity of the ball.

Generating football Cd profiles without a wind tunnel

Wind tunnels have been used extensively to obtain the aerodynamic characteristics of many objects, including sports balls. However, as an expensive piece of equipment, wind tunnels are not always appropriate. This paper describes a method which was used to obtain a football’s coefficient of drag (Cd) profile without the use of a wind tunnel. A football was launched at a variety of velocities and its flight recorded with high speed video cameras in 2D. An aerodynamic model was used to generate a series of displacements to compare with the recorded trajectories. In order to simulate aerodynamic drag, a sigmoid function was developed which mimics the shape of a typical aerodynamic profile. A simplex optimisation process was used to generate a number of Cd profiles which result in a minimum error between the modelled and recorded displacements. It was found that the ball had a Cd of around 0.275 in the turbulent regime and 0.525 in the laminar.

Self-Reported Symptoms of Exercise-Induced Asthma in Korean National Team Athletes

The prevalence of exercise-induced asthma (EIA) increases markedly in elite athletes. EIA has been extensively studied in Caucasian athletes, but little report has been published in Asian Athletes. PURPOSE: To investigate the prevalence of EIA symptoms, asthma diagnosis, and asthma medication using a validated questionnaire in Korean national team athletes by sex, and types of sports. METHODS: The study population was the year 2008 Korean national team athletes who were training at the Taeneung national training center. The questionnaire was composed of EIA symptoms (cough, wheezing, sputum production, chest tightness and difficulty of breathing), asthma diagnosis by a physician, and asthma medication. EIA symptoms were analyzed by sex and types of sports (record, ball and martial art) using chi-square test at p<0.05. RESULTS: Male (n=172; 24.2±4.3 yo) and female (n=117; 21.6±4.2 yo) athletes from 16 different summer sports completed the questionnaire. Cough (66.3%) and sputum production (62.1%) were often experienced while wheezing (30.9%) and difficulty of breathing (30.5%) were relatively not. None of EIA symptoms was self-reported by about 18% of all the participants, and all EIA symptoms were reported by 9.5%. Asthma diagnosis by a physician was reported 10.9% all the participants and use of asthma medication was only 6.7%. Cough, chest pain and difficulty of breathing were affected by sex. Negative response to cough was relatively less reported in female athletes and negative response to chest pain and difficulty of breathing was less reported in male athletes. Types of sports, especially martial art, affected the prevalence of cough and wheezing. Types of sports, especially martial art, affected the prevalence of cough and wheezing. CONCLUSIONS: Asthma prevalence in Korean athletes was similar to Caucasians. High prevalence of EIA symptoms was found in Korean athletes. This study also suggests sex and types of sports may influence the prevalence of EIA symptoms.

A7 スポーツ用ボールのスピンを伴う飛翔映像の自動画像処理(空力特性II)

A7 スポーツ用ボールのスピンを伴う飛翔映像の自動画像処理(空力特性II)

A-12 スポーツ用ボールの剛体壁面への斜め衝突における初期スピンの影響(テニス・バドミントン1)

A-12 スポーツ用ボールの剛体壁面への斜め衝突における初期スピンの影響(テニス・バドミントン1)

Sports ball aerodynamics: A numerical study of the erratic motion of soccer balls

The application of the commercial CFD code, FLUENT, to sports ball aerodynamics was assessed and a validated 3D analysis technique was established for balls that have been scanned with a 3D laser scanner or drawn in CAD. The technique was used to examine the effects of surface geometry on the aerodynamic behaviour of soccer balls by comparing the flow around different balls and predicting the aerodynamic force coefficients. The validation process included performing CFD studies on 3D smooth spheres and various soccer balls, and comparing the results to wind tunnel tests and flow visualisation. The CFD technique used a surface wrapping meshing method and the Reynolds Averaged Navier–Stokes approach with the realizable k-ε turbulence model, which was found to be able to predict the drag, lift and side force coefficients ( C D , C L and C S ) reliably, to compare the wake behaviour, and to give good pressure distributions near the stagnation point. The main limitations of the technique with the available computational resources were its inability to accurately predict boundary layer transition or growth, but despite this, several conclusions could be drawn regarding soccer ball aerodynamics. C D was not significantly different between balls. C L and C S were found to be significantly affected by the orientation of the ball relative to its direction of travel, meaning that balls kicked with low amounts of spin could experience quasi-steady lift and side forces and move erratically from side-to-side or up and down through the air. For different balls, C D , C L and C S were predicted and their variation with orientation entered into a modified trajectory simulation program. The erratic nature of this type of kick was found to vary with details of the surface geometry including seam size, panel symmetry, number, frequency and pattern, as well as the velocity and spin applied to the ball by the player. Exploitation of this phenomenon by players and ball designers could have a significant impact on the game.

Tennis physics, anyone?

After a tennis ball lands on the court, it slows down, spins up, and squashes. Friction on the ball can even reverse direction, pushing it forward.

Experimental studies of the aerodynamics of spinning and stationary footballs

The accurate discrimination of the aerodynamic parameters affecting the flight of sports balls is essential in the product development process. Aerodynamic studies reported to date have been limited, primarily because of the inherent difficulty of making accurate measurements on a moving or spinning ball. Manufacturers therefore generally rely on field trials to determine ball performance, but the approach is time-consuming and subject to considerable variability. The current paper describes the development of a method for mounting stationary and spinning footballs in a wind tunnel to enable accurate force data to be obtained. The technique is applied to a number of footballs with differing constructions and the results reported. Significant differences in performance are noted for both stationary and spinning balls and the importance of the ball orientation to the flow is highlighted. To put the aerodynamic data into context the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air. The aerodynamic differences are shown to have a considerable effect on the flight path and the effect of orientation is shown to be particularly significant when a ball is rotating slowly. Though the techniques reported here are applied to a football they are equally applicable to other ball types.

Aerodynamic Instability of Bluff body on Sports Ball Flight

Aerodynamic Instability of Bluff body on Sports Ball Flight

A12 スポーツボールに作用する定常空気力の精密測定用空気軸受け天秤の開発 : 大気圧変動の影響の除去について(ボール)

A12 スポーツボールに作用する定常空気力の精密測定用空気軸受け天秤の開発 : 大気圧変動の影響の除去について(ボール)

A new measure of roughness for defining the aerodynamic performance of sports balls

A new analysis is presented of the major findings in sports ball aerodynamics over the last 20 years, leading to a new method for defining surface roughness and its effects on the aerodynamic performance of sports balls. It was shown that the performance of balls in soccer, tennis, and golf are characterized by the position of the separation points on the surface of the ball, and that these are directly influenced by the roughness of the surface at a given Reynolds number and spin rate. The traditional measure of roughness k/D (the ratio of surface asperity dimension to diameter) was unable to predict the transition from laminar to turbulent flow for different sports balls. However, statistical measures of roughness commonly used in tribology were found to correlate well with the Reynolds number at transition and the minimum Cd after transition. It was concluded that this new measure and a further one of dimension should allow the complete characterization of the aerodynamic performance of sports balls. The effects of surface roughness on spin rate decay were also considered, and it was found that tennis balls had spin decay over six times that of golf balls and was due to the increased skin friction of the nap.